I discovered an unexpected power flow mode while using the combination of LAUNCHXL-F28027 and BOOSTXL-C2KLED. I had jumpers installed on headers J2 and J8 of the Booster Pack, and I had jumpers installed on headers JP1, JP2 and JP3 of the Launch Pad. The Booster Pack and the Launch Pad were connected together. These jumpers were in place for development of a stand-alone application, i.e. the 12 V supply was connected but the USB cable was not connected. My stand-alone application worked fine, as expected.
Then I decided to make a change to my code. I unplugged the 12 V supply, expecting as a result that it would be impossible for the boost converters and RGB LEDs to receive power. I then connected the USB cable to modify the code that I wanted to be programmed into flash memory. My original code in flash memory began executing as soon as the USB cable was connected, which I anticipated, but to my surprise the power stage was powered up as well. I examined the V+ supply voltage in the expressions window, and found it to be 4-5 V depending on the current demand. In other words, it seems that the TPS40200 circuit intended to power the 5 V line from the 12 V supply during stand-alone operation was allowing the V+ supply line to receive power from the 5 V supply line of the USB connection when modifying code. My mistake, of course, was that I should have removed the jumper on JP3 before connecting my un-powered target system to the USB cable (this jumper cannot simply be removed altogether, since it is necessary to achieve stand-alone operation). Although no damage occurred to either my USB port or the target hardware, I thought it might be a good idea to post this observation since it wasn't obvious to me that this type of reverse power flow mode could occur.
